Means for captivating a screw in an internally threaded supporting member



NOV- 27, 1952 E. R. CARLSON 3,066,271

MEANS FOR CAPTIVATING A SCREW 1N AN INTERNALLY THREDED SUPPORTINGl MEMBER Filed July e, 1959 ATTOR E United States Patent Olitice 3,066,271 Patented Nov. 27, 1962 MEANS FOR CAPTIVATNG A SCREW IN AN IN- TERNALLY THREADEEB SUPPGR'HNG MEMBER Ernest R. Carlson, Fairfield, Conn., assigner to Harvey Hubbell, Incorporated, Bridgeport, Conn., a corporation of Connecticut Filed July 6, 1959, Ser. No. 824,969

2 Claims. (Cl. 339-44) This invention relates generally to means for captivating a screw in an internally threaded supporting member and particularly in structural settings wherein it is not reasonably possible to have access to the free end of the screw shank, i.e. the end which is disposed within the internally threaded supporting member, to captivate it.

It frequently occurs in manufacturing various products having screws that it is desirable to mount a screw in an internally threaded supporting member in such a manner that after being initially mounted, it is captivated; that is, not capable of being removed by unscrewing in normal use of the product.

A particularly important product area in which this occurs is that including electrical connecting devices, and particularly grounding electrical connecting devices. A11 example of such a device a grounding electrical plug, and such plugs usually include a grounding contact having a terminal that has a binding screw which is used to attach a grounding electrical wire to the plug. In View of the fact that the binding screw is an important part of the grounding system, safety requirements dictate that it be captivated, and thereby preclude inadvertent removal, loss and subsequent use of the plug in an ungrounded manner. The general concept of captivating screws is known; however, the methods fo-r effecting captivation are normally such as to require access to the free end of the threaded screw shank. When dealing with electrical connecting devices, the free end of the threaded screw shank is normally not accessible, and therefore conventional screw captivating means and methods are not feasible. This is true because these electrical connecting devices usually comprise a body of electrical insulating material in which is embedded one or more screw supporting members in the form of inserts having elongated, internally threaded passageways to receive the threaded screw shank. Once an insert is embedded in the body and a screw is inserted in the insert, it is not possible to have access to the inner end of the insert passageway, where the free end of the screw is disposed, in order to captivate the screw.

It is an object of the invention generally to provide improved means for captivating screws in internally threaded supporting members, and particularly to provide improved means for captivating screws in electrical connecting device bodies.

The object of the invention in a general sense is accomplished by providing a screw supporting member having an elongated passageway with an internally threaded portion of reduced diameter for threadedly receivingthe threaded screw shank of the screw, and means disposed at the inner end of the passageway which cooperates with the free end of the threaded screw shank the first l, time the screw is inserted into the passageway and fully 1screw tightened therein to captivate the screw by deforming the free end of the screw shank so as to provide a radially extending portion thereat of larger external diameter than the internal diameter of the threaded portion of the passageway. The object of the invention in a particular sense is accomplished by preliminarily embedding the supporting member referred to in the preceding sentence in the body of an electrical connecting device prior to the insertion of the screw in the passageway of said member.

The above and other objects and further details of that which I believe to be novel and my invention Will be clear from the following description and claims taken with the accompanying drawing, wherein:

FIG. l is a rear plan view of a grounding electrical adapter plug which incorporates the invention;

FIG. 2 is a sectional View taken substantially on line 2-2 of FIG. l;

FIG. 3 is a front plan view thereof;

FIG. 4 is a sectional view taken substantially on line 4-4 of FIG. l;

FIG. 5 is an enlarged perspective view of one of the parts;

FlG. 6 is an enlarged sectional view of a screw and its supporting member showing the screw in different positions which it occupies during initial assembly and use in solid, dotted, and dot-dash lines, and

FIG. 7 is an enlarged perspective view of a modilied form of the part shown in FIG. 5.

Referring to the drawing, and particularly to FIGS. 1 4, there is illustrated a grounding electrical adapter plug which incorporates the instant invention. The illustrated plug generally comprises a body lll, a pair of polarized male electrical contact blades l2, and a male grounding contact blade i4. The illustrated plug, it should be clearly understood, is merely exemplary of one practical application of the invention in an electrical connecting device. The illustrated plug is designed to be received in an appropriate grounded electrical connecting device, such as a receptacle, having female contact means for receiving the male contact blades of the plug. The illustrated plug is adapted to have a threewire electrical cord, one of the wires of which is a grounding wire, connected to electrical terminal means of the plug. In addition, the illustrated plug includes female contact means for receiving a three-contact bladed grounding plug. Therefore, the illustrated plug is designed to effect two separate grounded connections to a grounded electrical connecting device having means for receiving only a single grounded three-contact bladed electrical plug.

The plug body 10 comprises a solid mass of electrical insulating material having a plurality of slots, passageways and recesses formed therein, as will be subsequently set forth. The plug body supports all of the other components of the plug, including the previouslymentioned male contact blades 12 and 14. The plug body is somewhat cylindrical and includes a generally flat front wall 16, a cylindrical side wall 18, and a flat, multiply recessed rear wall 20. A cut-out portion 22 is formed in the plug body in the vicinity of where a part of the front wall 16 intersects a part of the side wall 18. A circular opening 2.4 communicates with the cut-out portion 22, extends completely through the plug body, and communicates with a recess 21 in the 2t). Cut-out portion 22, opening 24 and rccess 21 permit the passage of an electrical cord from the front of the plug through the latter to the rear thereof, where the wires of the electrical cord may be connected to the terminal means of the plug, which is disposed at the rear of the plug body, as will become apparent.

A pair of spaced elongated slots 26, one being larger than the other to accommodate polarized male contact blades of an associated plug in a manner and for a purpose generally known in the electrical art, extend completely through the plug body 18 from the front to the rear thereof. The ront ends of the Slots are bevelled at 28 to facilitate insertion of the male contact blades of an associated plug, and the rear ends of the slots 26 communicate with irregularly shaped, shallow recesses 30 (see FIGS. 1 and 4), which in turn communicate with an enlarged recess 32 formed in the rear end of the plug body. A noncircular opening 34 having a bevel 36 is formed in the front wall 16 of the plug body 16 and communicates with an enlarged passageway 38 which extends to the rear completely through the plug body and communicates with an irregularly shaped recess 40, which in turn communicates with the previously mentioned enlarged recess 32 (see FIGS. 1 and 2). As can best be seen in PEG. 1,

the recesses 30 and 40 are spaced from each other, andV as can best be seen in FIG. 3, the slots 26 and opening 34 are kspaced from each other at` the front of the plug.

The slots 26 have laterally extending portions 42 which extend toward each other and which are disposed so as to extend from the rear of the plug body toward, but

short of, the front thereof (see FIG. 4). Adjacent, but spaced from, each ofthe slots 26 at the rear ofthe plug body there is disposed a generally cylindrical insert 44 which is rigidly secured to the plug body by being embedded therein. Inserts 44 include radially outwardly extending ribs 46 on the exterior thereof for facilitating embedding of the inserts in the plug body. Each insert 44 includes an elongated circular passageway 48 that is internally threaded.

Y Each insert 44 is intimately operatively associated with a contact spring 50 and one of the previously mentioned male contact blades 12. As can be most clearly seen in FIG. 4, each contact spring 5i) includes an acutely bent contact leg 52, an intermediate leg 54, and a perpendicularly bent mountingleg 56. Each contact spring mounting leg 56 includes an opening 58 that is arranged to surround a portion of van associated insert 44 and be adjacent one of the ribs 46. When the Contact springs are mounted on the plug body 1t), the contact spring legs 52 and 54 are positioned in the slots 26 and their enlarged portions 42 and the contact spring mounting legs 56 are disposed in the recesses 30. Adjacent each of the contact spring mounting legs 56 is disposed a bent mounting leg 60 of a male contact blade 12. Each of the mounting legs 60 includes an opening 62 which surrounds a portion of its associated insert 44. When assembled, the mounting legs 60 yare also disposed in the recesses 30. Each associated pair of contact spring mounting legs 56 and male contact blade mounting legs 68 is rigidly retained on its associated insert 44 by the flanged-over end 64 of the insert.

A headed binding screw 66 is threadedly mounted in each Iof the (inserts 44. Each associated male contact blade 12, insert 44, binding screw 66 and Contact spring 50 comprises acontact assembly. Each contact assembly is capableof (l) being electrically connected to a male electrical contact of an associated plug which is inserted through a slot 26 and contacts the bent leg 52 of a contact spring'SO, it being vnoted in this regard that beads 68 which are formed on bent legs 52`enhance such contact; (2) being electricallyconnected to a female contact of an electrical connector, such as a receptacle, to which the plug is connected by having its male contact blade 12 inserted therein, and (3) having an electrical wire (not shown) electrically connected `to the terminal 'formed-byV the headed binding screw 66, insert 44, contact spring leg 56 and male contact blade leg 60. All of the parts of the contact assemblies are made of good electrical conducting materials, preferably metallic materials, and for general operating convenience the contact spring 50 is made of a springy metallic material.

rhe illustrated plug includes a grounding' contact assem ly which comprises the previously mentioned male grounding contact blade 14 which has a generally U- shaped cross section and a bent mounting and terminal wall 76 that is rigidly connected to a hat contact wall 72, as by the rivet 74 (see PEG. 2). The grounding contact assembly also includes a female contact 76 in the form of a resilient U-shaped clip which is rigidly connected to the contact wall 72, as by rivet '78. When the grounding contact assembly is fully assembled on the plug, the female contact 76 is disposed in the passageway 38, its positioning therein being facilitated by guide projections 88, and the contact wall 72 and mounting and terminal wall 70 are disposed in the recess 40.

The grounding contact assembly is intimately .operatively assocated with an insert 82 which is Securely embedded in the plug body 10. Insert 82 is unitary, generally cylindrical and is provided with radially extending portions (not shown) to facilitate embedding and an elongated circular passageway 84. A portion 86 of the insert 82 extends into the recess 4t) and is rigidly connected to anV end portion 88 of the male contact blade mounting and terminal wall 70 by extending through an opening 90 which is formed in the end portion 88, and having its free extremity anged over to rigidly connect the parts. The insert 82 has an inwardly extending internally threaded portion 92 disposed adjacent the portion 86. The internal diameter of the threaded portion 92 is less than the internal diameter of the remainder 94 of the passageway 84, which is plain.

Adjacent and closing the interior end 96 of the insert 82 there is disposed a solid plug-like member 98, which will hereinafter be referred to as an anvil, which'is shown by itself in FIG. 5. The anvil 98 is generally cylindrical and comprises a cylindrical portion 100 that is disposed in and frictionally engages the inner surface of the insert end 96, a radial flange 102 which contacts the axial end of the insert end 96, and the reduced diameter portion 184 which is embedded in the plug body 10. The face of the Vanvil 98 is disposed within the insert 82 and comprises a at annular wall 106 which is located in a planerthat is Vperpendicular to the axis of the insert 82, and a central conicalrecess 108 that is po-sitioned within the wall 106. The anvil 98 comprises means for automatically captivating a binding screw in the insert 82 on its initially being inserted into the insert and fully tightened therein, as will Vbecome apparent. Y

A headed binding screw 110 is adjustably received in the insert 82 so as to be capable of selective manual longitudinal adjustment therein. However, after its initial mounting in the insert 82, the binding screw 110 is Capti- V'ated, i.e. not capable of being removed therefrom thereafter in normal use of the plug. When the parts of the plug are fully assembled, as shown in FlG. 2, the binding screw 110 has its head 112, which is illustrated as being hexagonal and having a kerf 114 formed therein, 'accessible for receiving an adjusting implement, such as a screwdriver, to'selectively manually adjust the position of the screw V11) in the insert 82. The screw 110 includes a shank 116 which is threaded over its entire axial extent. A conical recess 118 is formed inthe free end of the screw shank 116, i.e. the'end which is opposite the screw head 112.

ical recess y108 formed in the anvil 98. The free end of the screw shank 116 has a radially outwardly extending lt should be vparticularly noted thattheconical recess 118 is signicantly larger in diameter than the con-- annular portion 120 that has an outer diameter in excess of the inner diameter of the threaded portion 92 of the o insertv v82. Therefore; the bindingscrew 110, ltftervt *i.Sj

fully` assembled in the insert 82, as illustrated in FIG. 2, is capable of being selectively adjusted manually so as to withdraw much of its shank 116 outside of the insert. However, it is captivated in the insert 82 because it is not capable of being fully withdrawn therefrom during normal use of the plug due to the interference engagement of the screws radially extending portion 120 and the axially facing annular shoulder 122 formed by the axial inner end of the innermost thread of the inserts threaded portion 92. It will, therefore, be apparent that when fully assembled, the binding screw 110 is captivated in the insert 82. Captivated screws are highly desirable in many practical applications. It is particularly desirable in a grounding electrical plug, such as the illustrated plug adapter, wherein the binding screw 110 and the associated parts of the grounding contact assembly comprise vital elements in the grounding system for the plug, that the screw 110 be captivated. Prudence and safety requirements dictate that the binding screw 110 be irremovably mounted in order that it might not be inadvertently withdrawn from the insert 82, which is possible if it were not captivated therein, lost, and thereafter the plug used in an ungrounded manner.

My invention provides means for automatically captivating the binding screw 110 in the insert 82 by forming the radially extending portion 120 at the free end of the binding screw shank 116 on the occurrence of the initial insertion of the screw 110 into the insert 82 and the tightening of the screw therein. Reference to FIG. 6 will facilitate an understanding of the manner in which this occurs. In FIG. 6 the insert 82, anvil 98, and binding screw 110 are illustrated in solid lines in the positions and configurations which they are in at the time of initial insertion and assembly of the screw 110 into the insert 82. At this time, it should be carefully noted, the exterior surface of the screw shank 116 is threaded, but generally cylindrical throughout its entire length, the radially extending portion 120 not yet having been formed, and therefore, it is capable of clearing and being threadedly inserted into the insert 82 through the threaded portion 92 of the latter. At this time in assembly, the screw shank 116 has a flat, radially extending annular wall portion 124 formed around the recess 118 which faces the anvil 98. It should be particularly noted in FIG. 6, that the screw recess 118 is of larger diameter than the anvil recess 108 and that the flat annular wall 124 of the screw shank is narrower than and disposed to make planar contact with the flat annular wall 106 of the anvil.

In FIG. 6, the free end of the screw shank is shown in dotted lines in the condition that it assumes at the time of the initial insertion and full tightening of the screw 110 in the insert 82. Planar contact of the flat, annular, radially extending walls 124 and 106 results in the upsetting and deformation of the first thread of the screw at the free end thereof into the radially extending annular portion 120. This occurs because the relatively thin, flat annular wall 124 of the screw shank yields to the relatively wide, flat annular wall 106 of the anvil on the occurrence of forced movement of the screw against the anvil. The anvil recess 108 provides a clearance for the central portion of the adjacent end of screw shank 116 during formation of the radially extending annular portion 120. As illustrated in FIG. 6, this clearance does not appear necessary; however, it sometimes is, as when a screw without a recess 118 is inadvertently used, and therefore, the recess 108 is provided. After the radially extending portion is formed on the screw shank 116, the binding screw 110 is captivated in the insert 82.

As pointed out above, the screw 110 is capable of being selectively manually adjusted longitudinally of the insert 82. However, in the event of a sufficient amount of adjustment of the screw 110 in the direction to withdraw the screw out of the insert 82, complete withdrawal of the screw out of the insert is prevented by the interference enof the radially extending PGOIl 12 Uf the screw with the axially facing shoulder 122 of the insert threaded portion 92, as is shown in dot-dash lines in FIG. 6.

In FIG. 7 there is illustrated a modified form of anvil 126 which may be substituted for the anvil 98 illustrated in FIGS. 1-6. The major difference between the anvils is that in the FIG. 7 modification, the face 128 of the anvil, which opposes the free end of the screw shank when these parts are operatively associated, includes a raised,

axially extending projection 130, instead of a recess as in the case of anvil 98. When the anvil 128 is utilized 1n place of the anvil 98, captivation of a binding screw which corresponds to screw occurs on its initially being inserted and fully tightened as a result of its recessed shank end being upset and deformed by the projection 130 into a radially extending portion which corresponds to portion of binding screw 110 in FIGS. 1-6. Both forms of anvils have proved to be successful in practice; however, the FIG. 5 form is preferred. Regardless of the form of anvil used, after the binding screw is initially mounted and captivated, it is thereafter incapable of being removedv in normal usage. This is useful in many practical applications, and particularly in grounded electrical connecting devices, wherein it is desirable that the grounding binding screw not be removable, as pointed out above.

In view of the foregoing it should be apparent that improved means for captivating screws in internally threaded supporting members have been generally provided and that they are of general utility, and that an improved grounding electrical connecting device having a captivated terminal binding screw which is part of the grounding system of the device has been provided which satisfies a particular need in grounded electrical connecting devices.

As will be evident from the foregoing description, certain aspects of my invention are not limited to the particular details of construction of the examples illustrated, and I contemplate that various and other .modifications and applications will occur to those skilled in the art. It is, therefore, my intension that the appended claims shall cover such modifications and applications as do not de.- part from the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A grounding electrical connecting device comprising: a body of electrical insulation material; a pair of load-carrying contacts carried by said body; a grounding contact in addition to said pair of load-carrying contacts; a terminal including a binding screw operatively associated with said grounding contact and arranged to have a grounding wire attached thereto from the exterior of said body; said grounding contact and said terminal being electrically connected to each other and supported by said body; and means for irrernovably mounting said binding screw on said body whereby it may not be removed therefrom in normal use; said means comprising a unitary supporting member for said binding screw that is permanently embedded in said body and a screw-deforming anvil also embedded in said body adjacent to said supporting member; said anvil having a portion arranged for contacting and deforming the first screw thread on said binding screw the first time it is screwed fully into said supporting mernber; said supporting member having an elongated passageway formed therein which includes an internally threaded cylindrical portion; said binding screw comprising a cylindrical threaded shank adapted to be threadedly received in said cylindrical portion, a head at one end of the shank and a radially outwardly extending annular portion at the other end of the shank; said supporting member housing said radially outwardly extending portion and a variable amount of said shank, depending upon the relative positions of said supporting member and said binding screw; the internal diameter of said cylindrical portion being less than the external diameter of said radially outwardly extending portion whereby on withdrawal Amovement of saidbinding screw 1 from -said supportingV Amember said radially extending portion engages said cylindrical portion and thereby prevents further withdrawal movement of said binding screw; said-binding screw prior to being initially disposed in said supporting member being devoid of said radially outwardly extending annular portion; and said anvil Vhavinga portion disposed lWithinsaid supporting member in position-to `Contact and upset said other end of said shank'the first time said other end of said shank is screwed-into said supporting member to thereby form saidV radially `outwardly extending annularA portion.

2. A vdevice as defined in claim 1 wherein said -binding screw initially has a circular recess formed in the said other endof its shank andthe portionof said anvil that is disposed within said supporting member includes a raised 15 V8 projection that extends towardlan'd opposes the said other end ofsaid shank and is arranged to be engaged thereby to contact and -upset said other endthe` first time'said binding screw is screwed into the supporting member.

References Cited in the' le of thisrpatent UNITED STATES PATENTS 1,257,730 Moulthrop Feb. 26, 1918 1,482,765 Sanborn Feb. 5, 1924 1,801,937 Rathbun Apr. 12, 1931 FOREIGN PATENTS 137,972 -Australia Mar.`25, 1948 

